Reversible metallopolymer network

ABSTRACT

The invention provides a metallopolymer coordination network comprising one or more coinage or similar metals and in some embodiments, a glyme or glyme-equivalent. The composition has an amorphous polymer network that is significantly stronger than previously reported supramolecular hydrogels synthesized without glyme. Glyme chain length and water content strongly influence the mechanical, electronic, and optical behavior of the network.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/690,745, filed Nov. 21, 2019, now U.S. Pat. No. 10,875,970, issuedDec. 29, 2020, which is a continuation of U.S. patent application Ser.No. 15/368,232, filed Dec. 2, 2016, now U.S. Pat. No. 10,487,181, issuedNov. 26, 2019, which applications claim priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application Nos. 62/309,205, filedMar. 16, 2016 and 62/262,061, filed Dec. 2, 2015, which applications areincorporated herein by reference in their entirety.

GOVERNMENT SUPPORT

This invention was made with government support under Grant No. R21EB014520 awarded by the National Institutes of Health. The governmenthas certain rights in the invention.

BACKGROUND OF THE INVENTION

Gels are soft materials comprised of two coexisting phases: a solidcomponent (gelator) that immobilizes a fluid component by surfacetension. The gelator molecules can self-assemble to span the entiresample in a continuous, cross-linked network. In contrast to chemicalgels where the gelator is covalently linked through the entire system,physical gels interact non-covalently and can form reversible gels. Theintroduction of metal to the gelator provides alternative binding sitesto design and construct complex network architectures. The diversemetal-ligand coordination environments that induce the self-assemblyprocess influence gel properties. The resulting “metallogels” havegarnered ever-increasing interest in the fields of coordination polymergels and supramolecular polymer gels. Metallogels are highly versatilematerials with a wide range of applications in sensors, nanodevices,drug delivery, catalysis, and cosmetics.

Coinage metals (e.g., Cu, Ag, and Au) react with thiols to formstraight-chain polymers of 1:1 M(I):SR stoichiometry. These complexesare precursors for functional materials including metal nanoparticlesand supramolecular hydrogels. In various supramolecular hydrogels,metallophilic interactions drive self-assembly into two-dimensional (2D)sheets that stack in the third dimension to form lamellar structures.These gels are currently studied for their potential applications inmedicine, adhesives, and sensing. However, current metallogels requirevarious additives to regenerate after dehydration. The development of areversible metallogel that could be regenerated with only water wouldprovide a broad range of additional applications and advantages.

SUMMARY

A metallopolymer coordination network forms when organic moleculescoordinate to metal in the backbone of a metallopolymer. Changing thesize, composition, and shape of either molecule alters coordinationgeometry and shapes the molecular network, which provides control overelectronic, mechanical, optical, and physiochemical properties of thematerial. Rheological behavior is highly dependent on water content, andthe material can adopt a variety of solid forms depending on how and towhat extent water is removed. Rehydrating the vitrified material formsthe gel phase, granting the material unique healing capabilities.

The invention provides a reversible metallopolymer coordination networkof hard block (e.g., polycarboxylate) and soft block (e.g., polyethyleneoxide) polymers that are crosslinked by hydrogen bonds in water. Theviscoelastic fluid can be vitrified to multiple physical morphologies,and the resulting resin is water soluble, granting the material theability to self-heal. Bulk properties of the material are tuned byvarying length, shape, and composition of the polymers as well as thevitrification process.

The invention thus provides a reversible metallopolymer coordinationnetwork in the form of a metallogel. The metallopolymer backbone (or“hard block”) of the metallogel can be a coinage metal-based polymerlinked by a sulfur-containing amino acid or other small molecule. Thefluid phase (or “soft block”) of the metallogel can be a small moleculeor polymer having a series of lone pairs of electrons for chelation, forexample, polyethylene oxide and/or polycarboxylate, which coordinatewith the coinage metal to form chelate moieties of the metallogel.

In some embodiments, the soft block comprises a glyme orpolycarboxylate. In another embodiment, the soft block comprises a glymealternative such as a compound of Formula A or B (described below), forexample, tetramethylethylenediamine (TEMED) or a derivative thereof. Inone specific embodiment, the soft block comprises monoglyme(dimethoxyethane).

Accordingly, the invention provides a metallopolymer coordinationnetwork composition comprising a metallopolymer coordinated to one ormore compounds of Formula A:

wherein

X is O or NR′ wherein R′ is H, alkyl, aryl, alkenyl, alkynyl, aromaticheterocycle, or non-aromatic heterocycle;

R¹ and R² are each independently OH, alkoxy, or N(R^(a))₂ wherein eachR^(a) is independently H or (C₁-C₈)alkyl; and

n is 1, 2, 3, 4, or about 5 to about 50;

wherein the metallopolymer is a polymer of coinage metal atoms linkedtogether by sulfur groups of molecules comprising a carboxy or aminofunctional group, and the composition is water soluble and electricallyor ionically conductive.

In one embodiment, the composition further comprises water. Suchcompositions are therefore reversible aqueous gels. The gel hasnon-lamellar properties which can be restored after rehydration of thedehydrated gel. The composition has metal coordination sites for one ormore of the coinage metal atoms which can be partially saturated, orsaturated with moieties of Formula A. The elasticity of the gel rangesfrom about 15 MPa to about 40 MPa.

The molecules comprising the sulfur groups linking the coinage metalscan be sulfur-containing diacids, amino acids, dipeptides, tripeptides,oligopeptides, or polypeptides. Preferably, the molecule comprises acarboxy functionality or an amino functionality. In certain specificembodiments, the sulfur groups linking the coinage metals comprisethiomalic acid, glutathione, cysteine, or thioacetic acid.

In some embodiments, the compound of Formula A is 1,2-dimethoxyethane,diethylene glycol dimethyl ether, triethylene glycol dimethyl ether,tetraethylene glycol dimethyl ether, polyethylene glycol having an Mn ofabout 200-400, monomethyl polyethylene glycol having an Mn of about200-400, dimethyl polyethylene glycol having an Mn of about 200-400,1,4-dioxane, or tetramethylethylenediamine (TEMED).

The composition can include a complex of Formula IG:

wherein

each M is copper, gold, or silver;

each R is a sulfur-containing molecule wherein its sulfur atom is shownbonded to M groups of Formula IG; and

X is O or NMe; or wherein two or more moieties containing X form a groupcoordinated to the metals of the metallopolymer. The composition iswater soluble and can be electrically or ionically conductive

In some embodiments, M is copper. In other embodiments, M is gold. Inyet other embodiments, M is silver.

In certain specific embodiments, R—S is thiomalic acid, glutathione,cysteine, or thioacetic acid.

In one specific embodiment, X is O. In another specific embodiment, X isNMe.

In one embodiment, the composition comprises about 40 wt % to about 60wt % water, wherein the composition is a viscous fluid. In anotherembodiment, the composition comprises about 15 wt % to about 40 wt %water, wherein the composition is a stable gel. In yet anotherembodiment, the composition comprises about 0.1 wt % to about 15 wt %water, wherein the composition is an amorphous solid.

In other embodiments, the elasticity of the metallopolymer is modifiedby additives in the composition, wherein the additive is bipyridine,phenanthroline, neocuproine, or polyvinyl alcohol.

The invention also provides a composition prepared by combining ametallopolymer having carboxy or amino functional groups, or acombination thereof, and a molar excess of glyme, or a molar excess of anitrogen-glyme equivalent, in water, to provide a metallopolymercoordination network composition wherein the composition is anon-lamellar gel.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings form part of the specification and are includedto further demonstrate certain embodiments or various aspects of theinvention. In some instances, embodiments of the invention can be bestunderstood by referring to the accompanying drawings in combination withthe detailed description presented herein. The description andaccompanying drawings may highlight a certain specific example, or acertain aspect of the invention. However, one skilled in the art willunderstand that portions of the example or aspect may be used incombination with other examples or aspects of the invention.

FIG. 1A-B. Linear absorption of samples prepared from reagents listed inTable 1. (a) Comparison of peak absorbance between materials made withCu, Ag, and Au, along with pictures of each material; (b)gold-glutathione (Au-SG) and silver-cysteine (Ag-Cys) as examples ofmaterials made with other thiols. Data presented were smoothed underSavitzky-Golay method with a 10-point window.

FIG. 2. Time sweep rheometry of Cu-TM/G1 shows elasticity increase asthe sample dries in ambient conditions.

FIG. 3A-G. Pictures of Cu-TM/G1 in various solid forms: (a) wire, (b)gel, (c) hard sphere, (d) powder, (e) rigid puck, (f) hollow sphere, and(g) foam.

FIG. 4A-C. Representative Cu-TM/G1 curves used to obtain data in Table2. (a) Time sweep on three separate samples prepared simultaneously. (b)Frequency sweep run at fixed strain (γ=0.1%). (c) Strain sweep run atfixed frequency (ω=1 Hz).

FIG. 5. Comparison of Cu-TM/Gn elastic moduli.

FIG. 6A-C. (a) XRD of the sample (upper line) only shows diffractionpeaks attributed to the sample holder (dashed lower line). (b) SAXSdisplays one feature (q=0.25) that is an artifact at the edge of thedetector; no other diffraction peaks are apparent. (c) SEM micrographsof Cu-TM/G1 display a uniform surface around cracks that formed as thesample dried. Scale bar is 1 μM for the top two images and 100 nm forthe bottom image.

FIG. 7. ¹H-¹H correlation spectroscopy of Cu-TM/G1 synthesized in D₂O.The peaks at 3.2 and 3.4 ppm correspond to G1 and all other peakscorrespond to metallopolymer. The absence of off-diagonal peaks betweenG1 and metallopolymer indicates that G1 interacts non-covalently withthe metallopolymer.

FIG. 8. Differential scanning calorimetry of freshly synthesizedCu-TM/G1 differentiates between free solvent water (low temperature) andwater trapped in the molecular network (high temperature). These peaksare attributed to water loss because they are irreversible and are notapparent in desiccated material. The sample pan was re-weighed after therun to determine 3.7 mg of water (59 wt %) was lost during theexperiment.

FIG. 9. Infrared spectroscopy of freshly synthesized Cu-TM/G1 (solidblue line) and after drying for 12 h (dashed green line). The peak at1548 cm⁻¹ (carbonyl stretch) does not shift in energy while the sampledries and implies that the carboxylate environment remains unchanged.The peaks at ˜1380 cm⁻¹ (glyme ether stretch) display a shift inrelative intensity, which indicate the local environment of glyme etherchanges while the sample dries.

FIG. 10A-B. Smoothed linear absorption (a) of Cu-TM/G1 while drying and(b) comparison between Cu-TM/Gn.

FIG. 11A-B. Raw linear absorption (a) of Cu-TM/Gn while drying and (b)comparison between Cu-TM/Gn. Data presented in FIG. 7-10 were smoothedunder Savitzky-Golay method with a 10-point window.

DETAILED DESCRIPTION

We have developed a novel and highly modular metallopolymer coordinationnetwork. It consists an organic molecule (containing carbon, oxygen, andnitrogen) and one inorganic molecule (containing metal atoms). Theorganic molecule may be simple or complex, and may be a small moleculeor a polymer. The small molecules and/or polymers interact and form amesh that is capable of trapping water through physical forces. Theamount of trapped water dictates how much the polymers interact andconsequently controls the properties of the polymer.

For instance, at 50% water the material is viscous like honey; at 20%water it forms a gel similar to hair gel; at 0-10% water it forms thinfilms, hard plastics, porous foams, or powders, depending on how thematerial is shaped while drying. Extrusion into alcohols can form wires,spheres, and other molded shapes. The resulting solids are incrediblyrigid and are comparable to conventional engineering plastics andrubbers. The solid phases can be rehydrated, either partially or wholly,to reform the gel or viscous phases, which is a novel healing mechanismsuitable for maintaining and recycling plastics. The material is alsovery stable in the solid form as long as it remains dry.

The material's properties are easily altered by changing the compositionof the polymers. The metal atom strongly influences material color andis expected to change rigidity (through metal-oxygen bonding) andelectrical conductivity. Changing the organic polymer chain lengthalters the rigidity of the material and has a minor effect on visibleabsorbance. A combination of these simple changes provides for amaterial with properties that can be tuned for specific applications.Changing other reagents, such as thiol (thiomalic acid, glutathione,cysteine, and the like) and base (lithium hydroxide, sodium hydroxide,and ammonium hydroxide, and the like), also provides an additionaldegree of tunability. Suitable materials for preparing the materialsdescribed herein include coinage metals (copper, silver, and gold) andthiols because they form a straight-chain polymer and interact with theorganic polymer through metal-oxygen coordination.

Therefore, described herein is a new approach for bindingmetallopolymers through unique interpolymer interactions to form ametallopolymer coordination network capable of immobilizing water toform a gel. In one system described herein, coinage metal-thiolatepolymers and glyme are mixed in aqueous media to form dativemetal-oxygen bonds between polymers. The conductivity and opticalabsorption of the resultant materials originate in the metallopolymer.Glymes act as bridges between metallopolymers, which dictates thedistance between neighboring metallopolymers to further shape materialproperties. Water can penetrate and expand the polymer network tofurther increase metallopolymer separation. This control over networkarchitecture allows the bulk material to adopt a variety of solidshapes.

The materials have unique optical, electronic, and mechanical propertiesdependent on composition and metallopolymer spacing. Increasing glymechain length results in a more flexible network and a softer material.Wet gels change color as they dry because the network contracts to bringmetallopolymers closer together. Perhaps most interesting is that thematerial appears to be either electrically or ionically conductivedepending on metallopolymer spacing. A contracted network gathersmetallopolymers in close contact and improves electrical conductivity,while an expanded network separates metallopolymers and allows ions toflow freely. The type of conductivity is thus chosen for specificapplications by shaping network architecture. These uniquestructure-dependent properties enable new applications as detailedbelow.

While the material is inherently conductive, it also acts as awater-soluble adhesive. Together with the ability to adopt a largevariety of solid forms, this provides potential applications inelectrically conductive adhesives, battery electrolytes, circuitry,electrical contacts, conductive inks, and transparent conductors.

Definitions

The following definitions are included to provide a clear and consistentunderstanding of the specification and claims. As used herein, therecited terms have the following meanings. All other terms and phrasesused in this specification have their ordinary meanings as one of skillin the art would understand. Such ordinary meanings may be obtained byreference to technical dictionaries, such as Hawley's Condensed ChemicalDictionary 14^(th) Edition, by R. J. Lewis, John Wiley & Sons, New York,N.Y., 2001.

References in the specification to “one embodiment”, “an embodiment”,etc., indicate that the embodiment described may include a particularaspect, feature, structure, moiety, or characteristic, but not everyembodiment necessarily includes that aspect, feature, structure, moiety,or characteristic. Moreover, such phrases may, but do not necessarily,refer to the same embodiment referred to in other portions of thespecification. Further, when a particular aspect, feature, structure,moiety, or characteristic is described in connection with an embodiment,it is within the knowledge of one skilled in the art to affect orconnect such aspect, feature, structure, moiety, or characteristic withother embodiments, whether or not explicitly described.

The singular forms “a,” “an,” and “the” include plural reference unlessthe context clearly dictates otherwise. Thus, for example, a referenceto “a compound” includes a plurality of such compounds, so that acompound X includes a plurality of compounds X. It is further noted thatthe claims may be drafted to exclude any optional element. As such, thisstatement is intended to serve as antecedent basis for the use ofexclusive terminology, such as “solely,” “only,” and the like, inconnection with any element described herein, and/or the recitation ofclaim elements or use of “negative” limitations.

The term “and/or” means any one of the items, any combination of theitems, or all of the items with which this term is associated. Thephrases “one or more” and “at least one” are readily understood by oneof skill in the art, particularly when read in context of its usage. Forexample, the phrase can mean one, two, three, four, five, six, ten, 100,or any upper limit approximately 10, 100, or 1000 times higher than arecited lower limit.

The terms “about” and “approximately” are used interchangeably. Bothterms can refer to a variation of ±5%, ±10%, ±20%, or ±25% of the valuespecified. For example, “about 50” percent can in some embodiments carrya variation from 45 to 55 percent. For integer ranges, the term “about”can include one or two integers greater than and/or less than a recitedinteger at each end of the range. Unless indicated otherwise herein, theterms “about” and “approximately” are intended to include values, e.g.,weight percentages, proximate to the recited range that are equivalentin terms of the functionality of the individual ingredient, thecomposition, or the embodiment. The terms “about” and “approximately”can also modify the end-points of a recited range as discussed above inthis paragraph.

As will be understood by the skilled artisan, all numbers, includingthose expressing quantities of ingredients, properties such as molecularweight, reaction conditions, and so forth, are approximations and areunderstood as being optionally modified in all instances by the term“about.” These values can vary depending upon the desired propertiessought to be obtained by those skilled in the art utilizing theteachings of the descriptions herein. It is also understood that suchvalues inherently contain variability necessarily resulting from thestandard deviations found in their respective testing measurements.

As will be understood by one skilled in the art, for any and allpurposes, particularly in terms of providing a written description, allranges recited herein also encompass any and all possible sub-ranges andcombinations of sub-ranges thereof, as well as the individual valuesmaking up the range, particularly integer values. A recited range (e.g.,weight percentages or carbon groups) includes each specific value,integer, decimal, or identity within the range. Any listed range can beeasily recognized as sufficiently describing and enabling the same rangebeing broken down into at least equal halves, thirds, quarters, fifths,or tenths. As a non-limiting example, each range discussed herein can bereadily broken down into a lower third, middle third and upper third,etc. As will also be understood by one skilled in the art, all languagesuch as “up to”, “at least”, “greater than”, “less than”, “more than”,“or more”, and the like, include the number recited and such terms referto ranges that can be subsequently broken down into sub-ranges asdiscussed above. In the same manner, all ratios recited herein alsoinclude all sub-ratios falling within the broader ratio. Accordingly,specific values recited for radicals, substituents, and ranges, are forillustration only; they do not exclude other defined values or othervalues within defined ranges for radicals and substituents.

One skilled in the art will also readily recognize that where membersare grouped together in a common manner, such as in a Markush group, theinvention encompasses not only the entire group listed as a whole, buteach member of the group individually and all possible subgroups of themain group. Additionally, for all purposes, the invention encompassesnot only the main group, but also the main group absent one or more ofthe group members. The invention therefore envisages the explicitexclusion of any one or more of members of a recited group. Accordingly,provisos may apply to any of the disclosed categories or embodimentswhereby any one or more of the recited elements, species, orembodiments, may be excluded from such categories or embodiments, forexample, for use in an explicit negative limitation.

The term “contacting” refers to the act of touching, making contact, orof bringing to immediate or close proximity, including at the cellularor molecular level, for example, to bring about a physiologicalreaction, a chemical reaction, or a physical change, e.g., in asolution, in a reaction mixture, in vitro, or in vivo.

An “effective amount” refers to an amount effective to bring about arecited effect, such as an amount of a reagent necessary to form aproduct in a reaction mixture. Determination of an effective amount istypically within the capacity of persons skilled in the art. The term“effective amount” is intended to include an amount of a compound orreagent described herein, or an amount of a combination of compounds orreagents described herein, e.g., that is effective to form products in areaction mixture. Thus, an “effective amount” generally means an amountthat provides the desired effect.

The term “substantially” as used herein, is a broad term and is used inits ordinary sense, including, without limitation, being largely but notnecessarily wholly that which is specified.

The term, number average molecular weight (Mn), is given its normalmeaning wherein Mn is defined as the quotient of total sample weightdivided by the total number of polymer molecules.

The term “alkyl” refers to a branched or unbranched hydrocarbon having,for example, from 1-20 carbon atoms, and often 1-12, 1-10, 1-8, 1-6, or1-4 carbon atoms. Examples include, but are not limited to, methyl,ethyl, 1-propyl, 2-propyl (iso-propyl), 1-butyl, 2-methyl-1-propyl(isobutyl), 2-butyl (sec-butyl), 2-methyl-2-propyl (t-butyl), 1-pentyl,2-pentyl, 3-pentyl, 2-methyl-2-butyl, 3-methyl-2-butyl,3-methyl-1-butyl, 2-methyl-1-butyl, 1-hexyl, 2-hexyl, 3-hexyl,2-methyl-2-pentyl, 3-methyl-2-pentyl, 4-methyl-2-pentyl,3-methyl-3-pentyl, 2-methyl-3-pentyl, 2,3-dimethyl-2-butyl,3,3-dimethyl-2-butyl, hexyl, octyl, decyl, dodecyl, and the like.

The term “aryl” refers to an aromatic hydrocarbon group derived from theremoval of at least one hydrogen atom from a single carbon atom of aparent aromatic ring system. The radical attachment site can be at asaturated or unsaturated carbon atom of the parent ring system. The arylgroup can have from 6 to 20 carbon atoms, for example, about 6-10 carbonatoms. The aryl group can have a single ring (e.g., phenyl) or multiplecondensed (fused) rings, wherein at least one ring is aromatic (e.g.,naphthyl, dihydrophenanthrenyl, fluorenyl, or anthryl). Typical arylgroups include, but are not limited to, radicals derived from benzene,naphthalene, anthracene, biphenyl, and the like.

The term “heterocycle” refers to a saturated or partially unsaturatedring system, containing at least one heteroatom selected from the groupoxygen, nitrogen, silicon, and sulfur, and optionally substituted withone or more groups as defined for the term “substituted”. A heterocyclecan be a monocyclic, bicyclic, or tricyclic group. A heterocycle groupalso can contain an oxo group (═O) or a thioxo (═S) group attached tothe ring. Non-limiting examples of heterocycle groups include1,3-dihydrobenzofuran, 1,3-dioxolane, 1,4-dioxane, 1,4-dithiane,2H-pyran, 2-pyrazoline, 4H-pyran, chromanyl, imidazolidinyl,imidazolinyl, indolinyl, morpholinyl, piperazinyl, piperidinyl,pyrazolidinyl, pyrazolinyl, pyrrolidine, pyrroline, quinuclidine,tetrahydrofuranyl, and thiomorpholine.

Aromatic heterocycles can be referred to as heteroaryl groups. The term“heteroaryl” refers to a monocyclic, bicyclic, or tricyclic ring systemcontaining one, two, or three aromatic rings and containing at least onenitrogen, oxygen, or sulfur atom in an aromatic ring. The heteroaryl canbe unsubstituted or substituted, for example, with one or more, and inparticular one to three, substituents, such as alkyl, halo, or hydroxylgroups. Typical heteroaryl groups contain 2-20 carbon atoms in the ringskeleton in addition to the one or more heteroatoms. Examples ofheteroaryl groups include, but are not limited to, 2H-pyrrolyl, furanyl,imidazolyl, indolyl, pyranyl, pyrazolyl, pyridyl, pyrimidinyl, pyrrolyl,quinolyl, thiazolyl, thienyl, triazolyl, tetrazolyl, and xanthenyl. Inone embodiment the term “heteroaryl” denotes a monocyclic aromatic ringcontaining five or six ring atoms containing carbon and 1, 2, 3, or 4heteroatoms independently selected from non-peroxide oxygen, sulfur, andN(Z) wherein Z is absent or is H, O, alkyl, aryl, or (C₁-C₆)alkylaryl.In some embodiments, heteroaryl denotes an ortho-fused bicyclicheterocycle of about eight to ten ring atoms derived therefrom,particularly a benz-derivative or one derived by fusing a propylene,trimethylene, or tetramethylene diradical thereto.

It will be appreciated that the compounds of the invention can containasymmetrically substituted atoms, such as, asymmetrically substitutedcarbon atoms, asymmetrically substituted sulfur atoms, asymmetricallysubstituted metal atoms, or any combination thereof. All chiral,diastereomeric, racemic forms and all geometric isomeric forms of astructure are part of this disclosure. For example, a metallopolymercomposition can comprise an (R)-cysteine substituent, an (S)-cysteinesubstituent, or both.

As used herein, a “thiol” refers to an organic compound that includes atleast one “—SH” group, which is typically a primary or secondary thiolgroup, and which can be used as a coinage metal ligand. The thiol can bea water-soluble thiol or organic-soluble thiol. Preferably, the thiolmolecule also includes a carboxylic acid or amine moiety.

Examples of suitable water-soluble thiols include, but are not limitedto, glutathione, cysteine, captopril, thiomalic acid (mercaptosuccinicacid), N-(2-mercaptopropionyl)glycine, p-mercaptobenzioc acid,m-mercaptobenzoic acid, penicillamine, (C₂-C₇)mercaptoalkanoic acidssuch as 6-mercaptohexanoic acid, and the like.

Examples of suitable organo-soluble thiols include, but are not limitedto, 2-phenylethanethiol (PET), 1-phenylethanethiol, benzyl mercaptan,thiophenol, (C₁-C₁₈)alkylthiols such as methanethiol, isopropyl thiol,t-butyl thiol, hexanethiol and dodecanethiol, (C₈-C₁₈)mercaptoalkanoicacids such as 11-mercaptoundecanoic acid, (C₃-C₈)mercaptocycloalkanessuch as cyclohexanethiol, dimercaptosuccinic acid, 2-mercaptoethanol,3-mercaptopropanol, 3-mercaptopropane-1,2-diol(2,3-dihydroxypropyl-mercaptan; thioglycerol), 1-adamantanethiol,1-naphthalenethiol, 2-naphthalenethiol, camphorthiol, and the like. Someorgano-soluble thiols such as those having a carboxylic acidfunctionality may become water soluble at high pH (e.g., above about 7,above about 7.5, or above about 8). Organo-soluble thiol derivativeshaving carboxy or amino functionalities related to the thiols of thisparagraph are commercially available or can be prepared synthetically,for use as the thiols of the compositions described herein.

Thiolates typically comprise about 1-30 carbon atoms and may have a widevariety of functional or substituent groups such as oxo (e.g., carbonyl,aldehyde, or ketone) moieties, carboxylic acids, anhydride moieties,ester moieties, amide moieties, cyano, nitro, inorganic acid derivatives(e.g., phospho and boro acids and derivatives) and their sulfur andamino analogs, including I^(o), II^(o), III, and IV^(o) amines,zwitterionic moieties, and various substituents where the substituentsmay be hydrocarbon or substituted hydrocarbon, as well as carbocyclicand heterocyclic, with functional groups coming within the groups setforth above, as well as nitrogen derivatives, such as azo, azoxy, anddiazo, organic and inorganic salts of the above ions, and the like.Complex thiolates may be used, both naturally occurring and synthetic,including oligomers, e.g., oligopeptides, of from about 2 to 30 units,thio analogs of purines, pyrimidines, nucleotides and nucleosides,aptamers, and amide linked nucleic acid analogs.

In some embodiments, the thiolates can be monomercapto thiolatesincluding thiol substituted carboxylic acids, e.g., p-mercaptobenzoicacid, and other mercaptoaromatic carboxylic acids of from 5 to 20,usually 7 to 20, carbon atoms and from 0 to 4 heteroatoms, carbocyclicor heterocyclic, generally having from 5 to 6 annular members, as wellas being optionally substituted by the above indicated groups, that maybe present as annular atoms or as substituents, mercaptoalkanoic acidsof from 3 to 20 carbon atoms, where the mercapto group is distant fromthe carboxy group, being separated by at least 2 carbon atoms, for a1-carboxy compound, at least at the 3-carbon, amino acids, e.g.,cysteine, mercaptobenzonitriles, tiopronin, glutathione, CoA,thiosugars, and the like. In some embodiments, one thiolate will bepreferred to another and various stabilities may be obtained dependingupon the particular thiolate used.

Glutathione (GSH) is a thiol and a naturally occurring and readilyavailable tripeptide. The tripeptide has a gamma peptide linkage betweenthe carboxyl group of a glutamate side-chain and the amine group ofcysteine, which is attached by normal peptide linkage to a glycine.

As used herein, the term “glyme” refers to a glycol ether. Onerepresentative example is dimethoxyethane. “Diglyme” refers todiethylene glycol dimethyl ether. Additional glymes include triglyme(triethylene glycol dimethyl ether) and tetraglyme (tetraethylene glycoldimethyl ether).

Glycol ethers can have, for example, a hydroxyl group, an alkyl group,or an ester group as a terminal group, while the other terminal group istypically an alkyl or phenyl group, but can also be a hydroxyl group.Examples of hydroxy-terminated glycol ethers include ethylene glycolmonomethyl ether (2-methoxyethanol, CH₃OCH₂CH₂OH), ethylene glycolmonoethyl ether (2-ethoxyethanol, CH₃CH₂OCH₂CH₂OH), ethylene glycolmonopropyl ether (2-propoxyethanol, CH₃CH₂CH₂OCH₂CH₂OH), ethylene glycolmonoisopropyl ether (2-isopropoxyethanol, (CH₃)₂CHOCH₂CH₂OH), ethyleneglycol monobutyl ether (2-butoxyethanol, CH₃CH₂CH₂CH₂OCH₂CH₂OH),ethylene glycol monophenyl ether (2-phenoxyethanol, C₆H₅OCH₂CH₂OH),ethylene glycol monobenzyl ether (2-benzyloxyethanol, C₆H₅CH₂OCH₂CH₂OH),diethylene glycol monomethyl ether (2-(2-methoxyethoxy)ethanol, methylcarbitol, CH₃OCH₂CH₂OCH₂CH₂OH), diethylene glycol monoethyl ether(2-(2-ethoxyethoxy)ethanol, carbitol cellosolve,CH₃CH₂OCH₂CH₂OCH₂CH₂OH), and diethylene glycol mono-n-butyl ether(2-(2-butoxyethoxy)ethanol, butyl carbitol,CH₃CH₂CH₂CH₂OCH₂CH₂OCH₂CH₂OH). Examples of dialkyl ether glycol ethersinclude ethylene glycol dimethyl ether (dimethoxyethane,CH₃OCH₂CH₂OCH₃), ethylene glycol diethyl ether (diethoxyethane,CH₃CH₂OCH₂CH₂OCH₂CH₃), and ethylene glycol dibutyl ether(dibutoxyethane, CH₃CH₂CH₂CH₂OCH₂CH₂OCH₂CH₂CH₂CH₃). Examples ofester-terminated glycol ethers include ethylene glycol methyl etheracetate (2-methoxyethyl acetate, CH₃OCH₂CH₂OCOCH₃), ethylene glycolmonoethyl ether acetate (2-ethoxyethyl acetate, CH₃CH₂OCH₂CH₂OCOCH₃),ethylene glycol monobutyl ether acetate (2-butoxyethyl acetate,CH₃CH₂CH₂CH₂OCH₂CH₂OCOCH₃), and propylene glycol methyl ether acetate(1-methoxy-2-propanol acetate).

Glymes further include polyethylene glycols of various lengths, forexample, the compounds of Formula A:

wherein X is O; R¹ and R² are each independently OH, OMe, OEt, SH, SMe,SEt, NH₂, NHMe, NMe₂, NHEt, NEt₂, PH₂, PHMe, PMe₂, PHEt, or PEt₂; and nis 1, 2, 3, 4, or about 5 to about 50 (e.g., PEG 400, and the like).

Additionally, various glyme alternatives (or glyme ‘equivalents’) can beused as part of the soft block for preparing metallogels, such asbipyridine, phenanthroline, neocuproine, polyvinyl alcohol, or thecompounds of Formula B:

wherein

X is O, S, CH₂, NH, NR¹ wherein R² is as defined for Formula A, or PH;

R¹ and R² are each independently OH, OMe, OEt, SH, SMe, SEt, NH₂, NHMe,NMe₂, NHEt, NEt₂, PH₂, PHMe, PMe₂, PHEt, or PEt₂; and

n is 1, 2, 3, 4, or about 5 to about 50 (e.g., PEG 400, and the like).

A “metallogel” is a metal-containing physical gel that has twocoexisting phases: (1) a solid component (gelator) that immobilizes (2)a fluid component by surface tension, wherein the gelator molecules canself-assemble to span the entire sample in a substantially continuous,cross-linked network. The two phases interact non-covalently and canresult in a reversible gel. The metal-containing gelator providesalternative binding sites for the fluid component.

The composition of the metallogel in this disclosure comprises ametallopolymer coordination network which, in various embodiments, has anon-lamellar structure (non-sheet forming structure, due in part to theamorphous nature of the disclosed metallopolymer) resulting in itsresistance to shearing. In some embodiments, the metallogel is capableof immobilizing water to form a non-lamellar aqueous gel with improvedelasticity such that the elasticity of the metallogel can range fromabout 5 MPa to about 100 MPa, for example, about 15 MPa to about 40 MPa,or about 25 MPa to about 35 MPa. The improvement in elasticity arises,for example, from the glycol units in the metallogel's composition.

Glycol moieties, for example, form a coordination complex with a centralatom or ion, which is usually metallic and is called the coordinationcenter. The surrounding array of bound molecules or ions are in turnknown as ligands or complexing agents. Ligands are generally bound tothe central atom by a coordinate bond (donating electrons from a loneelectron pair into an empty metal orbital, also known as a dative bond,represented by a hatched or dashed line in the Formulas), and are saidto be coordinated to the atom. A coordination complex whose center is ametal atom is called a metal complex.

The maximum coordination number for a certain metal is thus related tothe electronic configuration of the metal ion (the number of emptyorbitals) and to the ratio of the size of the ligands and the metal ion.When the metal's coordination sites are filled by ligands, for example,the oxygen atoms of a glycol moiety or the nitrogen atoms of anitrogen-glyme equivalent (nitrogen-glyme equivalent meaning the oxygenheteroatoms in the glyme are replaced with nitrogen heteroatoms, such asin TEMED for example) then the metal sites are saturated. Similarly, ifthe metal coordination sites of all the metals in a metallopolymer aremostly filled or filled then the metals in the metallopolymer arepartially saturated, substantially saturated or saturated.

Metal saturation can be achieved by adding a sufficient amount or anexcess amount of either a ligand or an additive, or combination thereofto the metallopolymer formulation chemistry. For example, the number ofmoles of glyme based on its molecular weight can be equivalent to or inexcess to the number of metal coordination sites calculated for thesynthesis of a metallopolymer. Alternatively, the synthesis of themetallopolymer can be based on the number of moles of the total numberof heteroatoms in the glyme added, or the number of moles of theheteroatoms available for coordination in the glyme added.

The metals, ligands, heteroatoms, and functional groups in themetallopolymer coordination network of this disclosure provideelectronic, hydrogen bonding, and Van der Waals interactions that trapor immobilize water molecules which result in formation of a gel in thehydrated metallopolymer having resilient elastic properties andself-healing properties even after many cycles of dehydration andrehydration.

The general synthesis of a metallopolymer in this disclosure is shown inEquation 1.

The synthesis is generally carried out by mixing an organothiol (R—SH)in base (B⁻) and contacting the mixture with a metal salt (MX_(a)) underaqueous conditions. A ligand (L:) is then added, optionally incombination with an optional additive. A metallopolymer suspension formswhich is collected as a gel, which may be desiccated to a desired adesired water content.

Embodiments of the Invention

In a first embodiment, a metallopolymer coordination network compositioncomprises a metallopolymer coordinated to one or more compounds ofFormula A:

wherein

-   -   X is O or NR′ wherein R′ is H, alkyl, or aryl; R¹ and R² are        each independently OH, alkoxy, or N(R^(a))₂ wherein each R^(a)        is independently H or (C₁-C₈)alkyl; and n is 1, 2, 3, 4, or        about 5 to about 50;        wherein the metallopolymer is a polymer of coinage metal atoms        linked together by sulfur atoms of sulfur-containing moieties,        wherein one or more of the sulfur-containing moieties comprise        carboxy or amino functional groups.

In other embodiments, the composition further comprises water. Thecomposition is a reversible gel. The gel has non-lamellar propertieswhich can be restored after rehydration of the dehydrated gel. Thecomposition has metal coordination sites for one or more of the coinagemetal atoms which can be partially saturated, or saturated with moietiesof Formula A. The elasticity of the gel ranges from about 15 MPa toabout 40 MPa.

In various embodiments, the metallopolymer composition can be dehydratedto a semi-solid or a solid, or the semi-solid or the solid can berehydrated to a gel or a fluid where the physical state of themetallopolymer interchanges reversibly from a metallopolymer fluid, ametallopolymer semi-solid, a metallopolymer solid, and a metallopolymergel when adding or removing water.

In various other embodiments, the compound of Formula A is1,2-dimethoxyethane, diethylene glycol dimethyl ether, triethyleneglycol dimethyl ether, tetraethylene glycol dimethyl ether, polyethyleneglycol having an Mn of about 200-400, monomethyl polyethylene glycolhaving an Mn of about 200-400, dimethyl polyethylene glycol having an Mnof about 200-400, 1,4-dioxane, or tetramethylethylenediamine (TEMED).

In a second embodiment, the sulfur-containing moieties (R—S) are linkedto the coinage metals (M) as shown in Formula I:

wherein

each A of Formula I is coordinated to M of Formula I; and each R—S is asulfur-containing diacid, amino acid, dipeptide, tripeptide,oligopeptide, or polypeptide.

In a further embodiment, each sulfur-containing moiety linking thecoinage metals of Formulas IA-IC comprise thiomalic acid, glutathione,or cysteine;

In additional embodiments, two or more moieties of A of Formula A arecross-linked between two proximal coinage metals or between two or moredistal coinage metals, or a combination thereof, as in Formulas ID-IF:

wherein m is 1 to 10.

The oxygen atoms in each glyme moiety or the nitrogen atoms in eachnitrogen-glyme equivalent moiety can coordinate to one or more metals indifferent configurations as shown in Formulas ID-IG as an example. Oneor more oxygen heteroatoms or one or more nitrogen heteroatoms of oneglyme or one nitrogen-glyme equivalent moiety may coordinate to onemetal in approximately a 1:1 ratio (the ratio of ligand to metal,Formula I). In other examples the ligand comprising more than oneheteroatom has a longer length to allow one ligand to coordinate to twoor more metals in the metallopolymer. The one longer ligand maycoordinate to two (Formula ID) or more adjacent metals (Formula IE), itmay coordinate to two or more metals that are spaced further apart as inFormula IF, or in all other possible configurations.

In a third embodiment, the composition comprises a complex of FormulaIG:

wherein

each M is copper, gold, or silver; each R is a sulfur-containing moietywherein its sulfur atom is linked to M of Formula IG; and X is O or NMe;or wherein two or more moieties containing X form a group coordinated tothe metals of the metallopolymer; wherein the composition is watersoluble and electrically or ionically conductive.

In some embodiments X is O, in other embodiments M is copper. Inadditional embodiments R—S is thiomalic acid, glutathione, cysteine, orthioacetic acid.

In certain embodiments, the composition comprises about 40 wt % to about60 wt % water, wherein the composition is a fluid. In other embodiments,the composition comprises about 15 wt % to about 40 wt % water, whereinthe composition is a gel. In yet additional embodiments, the compositioncomprises no water, or about 0.1 wt % to about 15 wt % water, whereinthe composition is a solid.

In any of the embodiments, the elasticity of the metallopolymercomposition of is modified by additives in the composition, wherein theadditive is bipyridine, phenanthroline, neocuproine, or polyvinylalcohol.

In a fourth embodiment, the composition of a metallopolymer isrepresented by Formula II:

wherein

each M is copper, gold, silver, tin, nickel, aluminum, or titanium; eachR is a sulfur-containing moiety comprising a carboxy or amino functionalgroup wherein its sulfur atom is linked to M of the metallopolymer ofFormula II; and one or more A moieties form Formula A:

wherein

X is O or NR′ wherein one or more X is coordinated to M of Formula II;R′ is alkyl, methyl, ethyl, propyl, butyl, pentyl, cyclopropyl,cyclobutyl, or cyclopentyl; R¹ and R² are each independently OH, alkoxy,or N(R^(a))₂ wherein each R^(a) is independently H or (C₁-C₈)alkyl; andn is 1, 2, 3, 4, or about 5 to about 50;

wherein the metallopolymer further comprises immobilized water.

In various embodiments, the composition is a non-lamellar gel comprisingabout 15 wt % to about 40 wt % water.

In embodiments of the gel, the elasticity ranges from about 15 MPa toabout 40 MPa.

In some particular embodiments, each M is copper or gold, each R—S isthiomalic acid or cysteine, each X is O, n is 2, 3 or 4, and R¹ and R²are H, alkoxy or (C₁-C₈)alkyl.

In other embodiments, the composition is electrically or ionicallyconductive.

In various embodiments of the composition, the number of repeating M-Smoieties ranges from about 3 to about 50, e.g., about 3-10, about 5-20,about 10-30, or about 10-50.

In a fifth embodiment, a composition can be prepared by combining ametallopolymer having carboxy or amino functional groups (for example,in the R group of Formulas I, Formulas IA-IG, or Formulas II), or acombination thereof, and a molar excess of glyme, or a molar excess of anitrogen-glyme equivalent, in water, to provide a metallopolymercoordination network composition wherein the composition is anon-lamellar gel.

Metallogels Through Glyme Coordination

It was discovered that coinage metal-thiolate polymers (CMTPs) formnovel materials when synthesized in the presence of aqueous polyethyleneglycol dimethoxy ethers (glyme, Gn). Glyme intercalation prevents theformation of 2D sheets normally observed in metal-thiolate complexes.Paradoxically, glyme incorporation strengthens the materials. Varyingglyme chain length and water content provides explicit control overmechanical strength and visible absorption. All coinage metals arecapable of forming homologous materials with a variety of thiolatescontaining carboxylic acid moieties (Table 1, FIG. 1). Copper-thiolatepolymers were found to be versatile starting materials for preparationof the novel materials. For simplicity, the copper-thiomalic acid(Cu-TM) system, found to be representative, is further described herein.

TABLE 1 Reagents useful for forming metallogels. Metal Salt Thiol Glymecopper(II) chloride dihydrate glutathione 1,2-dimethoxyethane(CuCl₂•2H₂O) (GSH) (G1) silver(I) nitrate thiomalic acid diethyleneglycol (AgNO₃) (TM) dimethyl ether (G2) gold(III) chloride trihydrateL-cysteine triethylene glycol (HAuCl₄•3H₂O) (Cys) dimethyl ether (G3)tetraethylene glycol dimethyl ether (G4) dimethyl polyethylene glycolM_(n)~250 (G~5)

Metallopolymer was prepared by mixing CuCl₂.2H₂O with thiomalic acid(TM) in a 1:3 molar ratio. Immediate addition of a large molar excess ofglyme precipitates a dense yellow phase (denoted as Cu-TM/Gn). Theisolated material is a viscous liquid that consists of ca. 50 wt %water. Dynamic rheological studies corroborate a marked increase inelasticity as water evaporates (FIG. 2).

Due to its hygroscopic nature, the material changes form as waterconcentration reaches equilibrium with the relative humidity (RH) of itsenvironment. After drying to ca. 30 wt % water the material exhibitsgel-like behavior by supporting its own weight and surviving the“inversion test” (Kumar and Steed, Chem. Soc. Rev., 2014, 43,2080-2088). The gels adopt a variety of solid forms contingent on howthe remaining water is removed: freeze-drying forms powders, dropcastingforms thin films, and thermal treatment forms porous foams (FIG. 3).Independent of its solid form, rehydrating the material to ca. 30 wt %water reforms the original gel phase.

Time-dependent mechanical properties were probed by oscillatory strainrheometry to quantify the elastic (G′) and viscous (G″) moduli of thematerials made with different glyme chain lengths. The gels were moldedinto rigid pucks by slow evaporation under 0% RH; this method isexpected to preserve the hydrogen-bonded structure of water trapped inhigh molecular weight glyme films (Gemmei-Ide et al., Langmuir, 2006,22, 2422-2425) and ensures homogeneity among samples. All samplesdisplay broadly similar behavior in each test. Rheometric properties aresummarized in Table 2 and representative curves can be found in FIG. 4.

TABLE 2 Cu-TM/Gn rheometric properties. Yield Point Sample G′ (MPa) G″(MPa) tan(∂) (%) Cu-TM/G1 32.5 ± 2.72 2.75 ± 2.18 0.0854 ± 0.0695 2.27Cu-TM/G2 30.8 ± 1.82 2.72 ± 1.63 0.0864 ± 0.0492 2.78 Cu-TM/G3 30.4 ±1.27 2.54 ± 1.62 0.0825 ± 0.0499 2.66 Cu-TM/G4  22.1 ± 0.505 0.735 ±0.251 0.0330 ± 0.0107 2.14 Cu-TM/ 17.3 ± 2.38  1.13 ± 0.243 0.0646 ±0.0056 5.41 G~5^([a]) ^([a])G~5: Mn ≈ 250 g mol⁻¹

G′ is approximately an order of magnitude greater than G″ within thelinear viscoelastic range, which validates the solid-like nature of thegel. Frequency sweep rheometry further confirms elastic behavior (G′>G″)over all time scales probed. The material behaves as a viscoelasticsolid at low strain amplitudes until the yield point (G′=G″) at 2-5%applied stress. At this point, the molecular network is disrupted andthe material starts to flow. Each sample shows an increase in G″ priorto the yield point, suggesting a change in the molecular structure thatresults in network disintegration.

Increasing glyme chain length results in a significant decrease inmagnitude of G′ (FIG. 5). Cu-TM/G1 affords the highest G′ at 32.5 MPa,and G′ decreases incrementally with increasing glyme chain length to17.3 MPa with Cu-TM/G˜5 (G˜5: M_(n)≈250 g mol⁻¹). The large overalldifference of 15.2 MPa indicates that longer glymes produce weakernetwork architectures. This relationship between glyme size and networkstrength suggests the existence of an ideal network that is preferentialtowards shorter glymes. Metallopolymer chain length cannot be preciselydetermined because the metallopolymer must be synthesized in thepresence of glyme to precipitate the material (vide infra). For thepurpose of this study, metallopolymer chain length is assumed to beapproximately equivalent across all Cu-TM/Gn because the ligand andsolution pH are constant throughout runs.

Network structure influences mechanical properties of materials. X-raydiffraction (XRD) (Liu et al., J. Mater. Chem., 2011, 21, 19214;Bensebaa et al., Langmuir, 1998, 14, 6579-6587; Bensebaa et al.,Canadian Journal of Chemistry, 1998, 1654-1659; Parikh et al., J. Phys.Chem. B, 1999, 103, 2850-2861) and small-angle X-ray scattering (SAXS)(Söptei et al., Colloids and Surfaces A: Physicochemical and EngineeringAspects, 2015, 470, 8-14) studies on CMTPs synthesized without glymeunderlie models of metallophilic interactions that enforcemetallopolymer self-assembly in 2D sheets. Scanning electron microscopy(SEM) studies are consistent with XRD and SAXS and furthermore revealporous 2D microplates. The boundaries between sheets in the resultinglamellar structures represent defect sites that may shear under externalforce. Typical G′ values are on the order of 10 Pa, though modificationthrough crosslinking can increase G′ up to thousands of Pascal whilemaintaining sheet structure (de Luzuriaga et al., J. Polym. Sci. Part A:Polym. Chem., 2015, 53, 1061-1066).

In the present system, XRD, SAXS, and SEM on glyme-containing CMTPs donot reveal sheet-like structures (FIG. 6). These studies jointlyindicate that glyme intercalation enforces an amorphous network.Metallophilic interactions underlie the 2D sheets previously observed(Söptei et al., Colloids and Surfaces A: Physicochemical and EngineeringAspects, 2015, 470, 8-14), indicating that glyme must be interactingwith the metallopolymer in a way that prevents this interaction andassembly. A model that accounts for this observation is one in whichglyme chelates the metal in the backbone of the metallopolymer (Scheme1).

This concept hinges on the chelation ability of glymes and is consistentwith recent work on polyether coordination to metals in multinuclearcomplexes (Mishra et al., Dalton Trans., 2012, 41, 1490-1502; Chevrieret al., Dalton Trans., 2013, 42, 217-231). Distortion of the metalcoordination sphere influences metallophilic interactions and preventsmetallopolymer assembly into sheets. G′ on the order of 10⁷ Pa suggeststhat the amorphous network is less susceptible to shear than previouslyreported CMTPs.

The metallopolymer is insoluble in neat glyme, but synthesis in thepresence of aqueous glyme allows the polymers to form a metallopolymercoordination network. ¹H-¹H correlation spectroscopy provides evidencethat polymer chains interact through non-covalent forces (FIG. 7). Waterconceivably permits glyme penetration into the metallopolymer networkand the large molar excess of glyme (e.g., 385 equivalents of G1 to Cu)subsequently drives precipitation of the material. The resulting viscousliquid consists of roughly 50% water, and differential scanningcalorimetry (DSC) indicates the presence of water as free solvent andtrapped in the network (FIG. 8). The degree of polymer interaction isdictated by water content: the network condenses as the material dries,resulting in increased elasticity and marked color changes.

Fourier transform infrared spectroscopy (FTIR) studies exhibit aconstant carbonyl stretch at 1548 cm⁻¹ as the sample dries (FIG. 9),which indicates that the carboxylate environment remains unchanged.There are two glyme ether peaks centered around 1380 cm⁻¹ that shift inintensity as the sample dries. This result implies that glyme exists intwo concentration-dependent forms and suggests the polymers are boundthrough metal-glyme coordination rather than carboxylate-glymeinteractions.

The concentration-dependence on network structure is observable throughchanges in visible absorbance, which is strongly influenced bymetallophilic interactions and the nature of the metal coordinationsphere. UV-Visible spectroscopy (UV-Vis) shows a single absorption(λ_(max)=414 nm) for Cu-TM/G1 as-synthesized, and periodic monitoring ofthe drying sample reveals a bathochromic shift (smoothed data in FIG.10a , raw data in FIG. 11a ). This is a characteristic of a change inthe metal coordination environment as water evaporates. The resultindicates the metal is initially ligated by water, and glymecoordination follows as water is lost and the network condenses.

Interestingly, varying glyme chain length in Cu-TM/Gn results in minimalchange in λ_(max) over the range of 403-418 nm (smoothed data in FIG.10b , raw data in FIG. 11b ). Such a minor change in linear absorptionsuggests that all glymes have similar coordination to the metal. Thisappears counter-intuitive, since binding affinity generally increaseswith glyme length and number of binding sites (Johansson et al.,Polymer, 1999, 40, 4399-4406; Terada et al., Phys. Chem. Chem. Phys.,2014, 16, 11737; Tang and Zhao, RSC Adv., 2014, 4, 11251). However, itis likely that the metal reaches coordinative saturation, where stericconstraints prevent coordination from all available oxygens. The limitedsolvent accessibility of the metal generates similar coordinationenvironments for all glymes independent of chain length.

Rheological studies support coordinative saturation and propose that G1produces the strongest network. Longer glymes introduce non-coordinatingoxygens that extend past the primary coordination sphere of the metal.This effectively produces polyethylene side chains that branch out intothe molecular network and add rotational degrees of freedom that bestowincreased flexibility. The tail ends of glyme could also coordinate twometal centers to create physical crosslinks between metallopolymers. Therelatively small differences in G′ between materials made with G1-G3indicate that these chains are too short to noticeably contribute tothis effect. The critical chain length appears to be G4, as there is asubstantial decrease in G′ upon G4 intercalation that continues withG-5. This complements the benchtop observation that longer glymes formmore fragile gels. It has not yet been determined whether this trendcontinues to longer glymes that could coordinate to three or more metalcenters, as this may strengthen the molecular network.

Thus, coinage metal-thiolate polymers form a metallopolymer coordinationnetwork when synthesized in the presence of glymes. The data supportthat glyme chelates the metal in the metallopolymer backbone. Thisinteraction prevents metallopolymer crystallization and results in awholly amorphous material that is stronger than previously reportedcoinage metal-thiolate supramolecular hydrogels synthesized withoutglyme. Varying glyme chain length and water content dictates the extentof polymer interaction and affects the mechanical and optical propertiesof the material. Though this report establishes a novel approach towardmetallopolymer gelation using Cu-TM/Gn systems, an extension to othercoordination metal polymers is currently under investigation.

Few other reversible interpenetrating or metallopolymer coordinationnetworks or resins are known to exist, all of which require moreextraneous variables (acidic conditions, UV-light) besides simply theaddition of water. The CMTP material described herein can exist in avariety of morphologies, which allows for a large variety ofapplications.

Commercial Applications

Commercial applications of glyme-mediated metallogel containing coinagemetal-thiolate polymers (CMTPGn) include (1) adhesives, (2) conductiveinks, (3) transparent conductors, and (4) electrolytes, among others.

1. Adhesives.

Adhesive properties of the material are being studied in theCoinage-TM/Gn system. Pull-off strength tests can be performed on avariety of substrates. XPS depth profiling and SEM studies can elucidatematerial surface structure and determine what substrates the materialcan bind to. Alterations to metallopolymer composition and networkarchitecture can increase bond strength and allow the material to adhereto new surfaces. Bond strength can be measured as a function ofhydration to determine the effects of a humid atmosphere. Plasticizerscan be used to moderate humidity effects and to develop new processingparameters. The deliverable product can be a cost-effective adhesivewith comparable bond strength to commercial adhesives. The product canbe fully functional in standard atmospheric conditions.

Due to the intrinsic electronic conductivity of the material, it canalso be used as an electrically conductive adhesive (ECA). Thesefunction as an alternative to tin-lead solder to provide a conductivepathway to connect one circuit element to another. Their application iscurrently limited because no commercialized ECAs can compete with theelectrical conductivity and impact strength of tin-lead solder. TheCoinage-TM/Gn system material is currently only known to bind to metaland glass surfaces. This disclosure provides compositions that be usedfor an ECA which has the electrical, mechanical, and thermal propertiesand additionally the impact strength needed for commercializationthrough alteration of metallopolymer composition and network structure.

2. Conductive Inks.

Conductive inks are electrically conductive liquids that are printeddirectly onto a substrate and cured in situ. The substrate can be anyobject the ink can adhere to, and the inks are commonly composed ofconductive materials like flaked silver or carbon nanomaterials. Printedelectronics are more economical than traditional industrial standardsfor many applications, such as RFID tags used in modern transit ticketsor windshield defrosters. Recently, conductive inks have found use inadditive manufacturing, which allows circuits to be printed inconjunction with plastics and obviates the need for conventional circuitboards.

The Coinage-TM/Gn system material is a viable conductive ink due to itsintrinsic electronic conductivity and is printable due to its tunableviscosity via plasticizers and varying water content. The deliverableproducts are 3D-printed circuits capable of self-healing through theaddition of water. Optimizing processing parameters of the material canprovide unique applications for extruded material.

3. Transparent Conductors.

Transparent conductors (TCs) are electrically conductive materials thatare highly transparent to visible light. This property allows currentcollection in solar cells, alteration of electrical charge inelectrochromic “smart windows,” and use in other optoelectronic devices.The most common TC, indium-tin-oxide (ITO), requires the scarce and veryexpensive element indium. Several other metal oxide semiconductors arehopeful alternatives to ITO, but they require further development ofdeposition techniques to enable the preparation of thin films.

The Coinage-TM/Gn system material is electrically conductive andinexpensive. It is trivial to form into thin films, and the addition ofplasticizers can allow for control over film morphology. The material istransparent, especially in thin films, though its color can decrease theability to transmit all visible light. Because color is a function ofmetallopolymer composition and network structure, tuning theseparameters can provide for a colorless, transparent material. Thedeliverable product is a very inexpensive TC made from earth-abundantmaterials that can find use in optoelectronics and dye-sensitized solarcells.

4. Electrolyte.

An electrolyte is an ionically conductive substance that allows the flowof ions between electrodes. In batteries, ions move from the cathode tothe anode when charging and in reverse on discharge. This processcompletes the circuit and allows the flow of electrons. A separator isan electric insulator that physically separates the cathode and anode toprevent a short circuit.

Although the subject of intense study, the ideal Li-ion batteryelectrolyte has not yet been developed. For a consumer battery system tofunction well a conductivity of at least 10⁻³ S cm⁻¹ at room temperatureis needed. Viscosity, salt concentration, ion association andion-solvent interactions must be optimized to maximize ion transport inelectrolytes. For the coinage-TM/Gn system material, viscosity and saltconcentration are easily controlled, while ion association andion-solvent interactions can be tuned through varying materialcomposition. As an added benefit, the metallogel can replace theseparator and electrolyte in one material since it can have no electricconductivity in this application. The deliverable product is a safer,cheaper battery with high ionic conductivity.

5. Further Applications.

The coinage-TM/Gn system material can also be used for seed coatings,seed tape, water-soluble packaging, tablet binders, gel capsulecoatings, controlled release matrix systems, bioadhesives, magneticpaints, protective coatings, and components for batteries, fluorescentlamps, and circuitry.

Methodology.

A general approach toward product development is to: (i) establishcomposition-dependent behavior of metallopolymer; (ii) shape networkarchitecture through structural adjustments to glyme; (iii) useplasticizers to augment desirable properties. As such, themetallopolymer composition establishes the fundamental properties of thematerial that are optimized through subsequent refinements of themolecular network.

The following Examples are intended to illustrate the above inventionand should not be construed as to narrow its scope. One skilled in theart will readily recognize that the Examples suggest many other ways inwhich the invention could be practiced. It should be understood thatnumerous variations and modifications may be made while remaining withinthe scope of the invention.

Examples

Materials.

All chemicals were obtained from commercial suppliers and used withoutfurther purification unless otherwise noted. Copper(II) chloridedihydrate (ACS Reagent, ≥99.0%), thiomalic acid (ReagentPlus, ≥99.0%),diethylene glycol dimethyl ether (ReagentPlus, 99%), tetraethyleneglycol dimethyl ether (≥99%), and poly(ethylene glycol) dimethyl ether(average M_(n)˜250) were obtained from Sigma-Aldrich. 1,2-Dimethoxyethane (99+% stab. with BHT) and triethylene glycol dimethyl ether (99%)were obtained from Alfa Aesar. Filters used were VWR syringe filters,0.2 μM cellulose acetate.

Instrumentation.

Oscillatory shear measurements were performed on a TA Instruments ARESrheometer. Dynamic frequency sweeps were performed for each sample usinga 0.1% shear strain (verified linear viscoelastic region) over afrequency range of 0.05 to 1000 rad s⁻¹. Strain sweeps were performedfor each sample at 1 rad s⁻¹ over a range of 0.01 to 90%.

Small angle X-ray scattering (SAXS) data were collected on a RigakuS-Max 3000 High Brilliance 3 Pinhole SAXS system outfitted with aMicroMax-007HFM Rotating Anode (CuKα), Confocal Max-Flux™ Optic, GabrielMultiwire Area Detector and a Linkham thermal stage. The feature atq=0.25 is an artifact at the edge of the detector.

X-ray diffraction (XRD) was performed on a Scintag X-2 AdvancedDiffraction system equipped with CuKα radiation (λ=1.54 Å). Scanningelectron microscopy (SEM) was performed on a JEOL JSM-6500F microscopeoperating at an accelerating voltage of 15 kV.

UV-Visible spectroscopy (UV-Vis) was performed on a Nanocrop 2000cSpectrophotometer on a 1-mm path length pedestal. Data were smoothedunder Savitzky-Golay method with a 10-point window to make trends moreapparent (raw data available in FIG. 4).

Example 1. Metallogels Through Glyme Coordination Cu-TM/G1 Synthesis

A 100 mM solution of thiomalic acid (1.2 mmol, 3 eq., in 12 mL 0.3 MNaOH) and 100 mM solution of CuCl₂.2H₂O (0.4 mmol, 1 eq., in 4 mL H₂O)were filtered. The thiol solution was added to the blue copper chloridesolution in a 50-mL polypropylene centrifugation tube and turned thesolution black. 1,2-Dimethoxyethane (G1, 12 mL) was immediately added,and the resulting cloudy white suspension was shaken at 4° C. for 45 minor until a dense yellow phase was apparent. After centrifugation at 3220g for 10 min at 4° C. the clear, colorless supernatant was siphoned offof the viscous yellow liquid. Only the bottom portion of the liquid wasused in experimentation to be sure no residual solvent was brought overinto the final product.

Cu-TM/G2-5 Synthesis.

All glymes studied (G2-G-5) are capable of substituting for G1 asdescribed for the synthesis of Cu-TM/G1. Other metal salts and thiolates(e.g., examples found in Table 1) are replaceable with one minoralteration to the synthetic method: 18 mL of glyme should be added whenusing glutathione or cysteine in place of thiomalic acid.

A 1:3 metal:thiol ratio is important to prepare optimally formedmaterial regardless of the metal oxidation state (i.e., 3 equivalents ofAgNO₃ are important to form Ag—SR/Gn despite Ag(I) already in thenecessary+1 oxidation state).

Example 2. Rheometry Sample Preparation

Immediately after its synthesis, 150 μL of the viscous liquid CMTP wastransferred into an 8-mm diameter rubber mold on parafilm. After dryingfor 24 h in ambient laboratory conditions it was transferred to adesiccator (RH=0%) and dried for another 24 h at ambient temperature andpressure. This method allowed water to slowly diffuse out of the gel toevaporate and prevented the material from cracking. The resulting puckfits perfectly under the 8-mm top plate on the rheometer. This methodprovided reproducible and accurate rheological measurement of thematerial.

While specific embodiments have been described above with reference tothe disclosed embodiments and examples, such embodiments are onlyillustrative and do not limit the scope of the invention. Changes andmodifications can be made in accordance with ordinary skill in the artwithout departing from the invention in its broader aspects as definedin the following claims.

All publications, patents, and patent documents are incorporated byreference herein, as though individually incorporated by reference. Nolimitations inconsistent with this disclosure are to be understoodtherefrom. The invention has been described with reference to variousspecific and preferred embodiments and techniques. However, it should beunderstood that many variations and modifications may be made whileremaining within the spirit and scope of the invention.

What is claimed is:
 1. A metallopolymer coordination network compositioncomprising a metallopolymer of Formula I:

wherein M is a coinage metal selected from copper, gold, silver, tin,nickel, and aluminum; and R—S is a sulfur-containing moiety; wherein themetallopolymer is a polymer of coinage metal atoms linked together bythe sulfur atoms of the sulfur-containing moieties, wherein one or moreof the sulfur-containing moieties comprise carboxy or amino functionalgroups.
 2. The composition of claim 1 further comprising water.
 3. Thecomposition of claim 1 wherein the composition is a reversible gel,wherein gel properties of the composition are restored after rehydrationof the corresponding dehydrated gel.
 4. The composition of claim 1wherein each M is copper, gold, or silver.
 5. The composition of claim 1wherein each R—S moiety of Formula I is a sulfur-containing diacid,amino acid, dipeptide, tripeptide, oligopeptide, or polypeptide.
 6. Thecomposition of claim 5 wherein the sulfur-containing moiety linking thecoinage metals comprises thiomalic acid, thioacetic acid, glutathione,or cysteine.
 7. The composition of claim 1 wherein the composition iselectrically or ionically conductive.
 8. The composition of claim 1comprising about 40 wt % to about 60 wt % water, wherein the compositionis a fluid.
 9. The composition of claim 1 comprising about 15 wt % toabout 40 wt % water, wherein the composition is a gel.
 10. Thecomposition of claim 1 comprising about 0.1 wt % to about 15 wt % water,wherein the composition is a solid.
 11. The composition of claim 1wherein the metallopolymer of Formula I is represented by Formula IB:

wherein R—S is a sulfur-containing moiety wherein the ratio (R—S):M is1:1; and Formula I is coordinated to one or more compounds of Formula A:

wherein each A of Formula IB is a Formula A moiety coordinated to M ofFormula IB; X is O or NR′ wherein R′ is H, alkyl, or aryl; R¹ and R² areeach independently OH, alkoxy, or N(R^(a))₂ wherein each R^(a) isindependently H or (C₁-C₈)alkyl; and n is 1, 2, 3, 4, or about 5 toabout
 50. 12. A metallopolymer composition of Formula II:

wherein each M is a coinage metal selected from copper, gold, silver,tin, nickel, titanium; and each R is a sulfur-containing moietycomprising a carboxy or amino functional group wherein its sulfur atomis linked to M of the metallopolymer of Formula II; wherein the ratio ofthe sulfur containing moiety and M is about 1:1, the metallopolymer is astraight chain metallopolymer further comprising immobilized water, andthe composition is electrically or ionically conductive.
 13. Thecomposition of claim 12 wherein the composition is a non-lamellar gelcomprising about 15 wt % to about 40 wt % water.
 14. The composition ofclaim 13 wherein each M is copper or gold, each R—S is thiomalic acid orcysteine, and the elasticity of the composition ranges from about 15 MPato about 40 MPa.
 15. The composition of claim 14 wherein the number ofrepeating M-S moieties is about 3 to about
 50. 16. A compositionaccording to claim 1 prepared by combining (a) an aqueous solutioncomprising a coinage metal salt and thiomalic acid, thioacetic acid,glutathione, or cysteine, and (b) a molar excess of glyme, or a molarexcess of a nitrogen-glyme equivalent, in water, for a sufficient periodof time to form a dense phase comprising the metallopolymer coordinationnetwork composition wherein the composition is a non-lamellar gel.
 17. Ametallopolymer material comprising a plurality of nanoparticles, a base,and water; wherein each of the nanoparticles is comprised of a pluralityof oligomer segments and each of the oligomer segments is comprised of athiol and a metal; and wherein the oligomer segments are coordinated toadjacent oligomer segments.
 18. The metallopolymer material according toclaim 17 wherein each oligomer segment is an M-SR oligomer, wherein M isa coinage metal and R is an organic moiety comprising a carboxy or aminofunctional group.
 19. The composition of claim 18 wherein each M iscopper, gold, or silver.
 20. The composition of claim 19 wherein R isthiomalic acid, thioacetic acid, glutathione, or cysteine.
 21. A methodfor forming a metallopolymer material: wherein the metallopolymermaterial comprises: a plurality of nanoparticles, a base, and water,wherein each of the nanoparticles is comprised of a plurality ofoligomer segments and each of the oligomer segments is comprised of athiol and a metal; and wherein the oligomer segments are coordinated toadjacent oligomer segments; the method comprising: combining (a) anaqueous solution comprising a coinage metal salt, base, and thiomalicacid, thioacetic acid, glutathione, or cysteine, and (b) a molar excessof glyme, or a molar excess of a nitrogen-glyme equivalent, in aconcentration of water, for a sufficient period of time to form a densephase; and equilibrating the concentration of water in the dense phaseto form the metallopolymer material wherein the metallopolymer materialis a non-lamellar gel.